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Do you always need a primary key?

Every table can have (but does not have to have) a primary key. The column or columns defined as the primary key ensure uniqueness in the table; no two rows can have the same key. The instance of the first table’s primary key in the second table is referred to as a foreign key.

No you can’t because Entity Framework needs to know the key to keep track on the object when you make an update or delete operation. There is a great difference between what EF can do with a database, and what is possible with a database. Most databases allow for a table to be without a primary key.

A primary key is mainly formally defined to aid referencial Integrity, however if the table is very small, or is unlikely to contain unique data then it’s an un-necessary overhead. Defining indexes on the table can normally be used to imply a primary key without formally declaring one.

A primary key constrain is a column or group of columns in a table that uniquely identifies every row in that table. The Primary key can’t be a duplicate, meaning the same value can’t appear more than once in the table. A table should have more than one primary key.

A primary key will always help with query performance. So if you ever need to query using the “key” to a “foreign key”, or used as lookup then yes, craete a foreign key. I don’t know. I have used a couple tables where there is just a single row and a single column. Will always only be a single row and a single column.

No, unless you can find an example of, “This database would work so much better if table_x didn’t have a primary key.” You can make an arguement to never use a primary key, if performance, data integrity, and normalization are not required.